A. Field of the Invention
This invention relates generally to computerized controllers of machine processes in a host machine such as an electrostatographic copies and particularly to controllers having capabilities for direct memory access of computer memory by the I/O device in the computer for output refresh and update of the host machine's control registers.
B. Prior Art
In the past, controllers having a computer would be able to access data in the computer memory only indirectly through the central processor which was relatively slow. The reason being that, the central processor would have control of the system bus thereby requiring the central processor to execute a program instruction for each access of data from computer memory thereby resulting in a relatively slow access rate of data from the computer memory to the control registers in the host machine. As the data being accessed from the computer memory used for refresh-update of the control registers is constantly being updated by the central processor to reflect the changing state of the ongoing machine processes, it is urgent that the updated control data be sent to the registers as soon as possible to reflect the current control state required of the machine process as perceived by the central processor and as recorded by the computer memory. Where the process to be controlled such as a machine process has many interrelated machine processes happening at a relatively high clock rate, then the problem of how to refresh and update the control registers in the host machine to reflect the state of the updated computer memory as quickly as possible to thereby guarantee accurate control of the ongoing process in the host machine becomes accordingly more acute. The particular embodiment described infra, a high-speed copying machine with critical parameters as the controlled process, is such an interrelated machine process having a need for accurate high-speed updating of its host machine's control registers.